This invention relates to a purification process for a polluted aqueous effluent to lower its chemical oxygen demand (COD).
Large volumes of polluted water from urban waste water, industrial effluents, and the treatment of biological liquids, such as liquid manure, cannot be discharged or reused without having undergone preliminary purification. Frequently, the purification treatment focuses on the elimination of nitrates, the polluting effects of which are significant and well known. However, nitrates are not the only polluting elements; many effluents should be purified even if they do not contain nitrates. Polluted aqueous effluents can, furthermore, come from aqueous media that initially contain nitrates and which have already been subjected to preliminary purification, resulting in the elimination of nitrates. In particular, for the treatment of biological waste, for example, nitrified liquid manure, there are processes which result in the almost-complete elimination of nitrates.
Various processes for the reduction of COD have been proposed, for example, for the treatment of waste water. JP-53-049858 relates to a process for the purification of waste water in which, after a biological treatment step, the effluents are treated by an adsorbing agent. This adsorbing agent is a dehydrated solid coprecipitate, such as the calcium aluminate obtained by the reaction of NaAlO.sub.2 and CaCl.sub.2. According to FR 2,671,791, it is possible to eliminate sulfate ions by precipitating the latter with calcium aluminates.